Tandem Pictet-Spengler-type cyclization and Smiles rearrangement have been discovered in the synthesis of pyrimidine-fused heterocycles.The reaction of 4-chloro-5-pyrrol-1-ylpyrimidine amino aldehyde with an amine under an acidic condition yielded the Pictet-Spengler-typecyclization product diazepine, which readily underwent Smiles rearrangement to give a novel pyrrolo[1,2-
f]pteridine derivative.